The deputy prime minister, Nick Clegg, is to undertake a hasty U-turn by dropping plans to make it easier for voters not to register to vote, following complaints that millions of voters might drop off the register.

The proposal has been criticised by the Electoral Commission, psephologists, Labour, and electoral registration officers. Jenny Watson, the Electoral Commission's chair, has warned that it could lead to as many as a third of voters falling off the register.

The electoral register is used to compile the list for jury service.

In a white paper published in the summer, the government proposed that as part of a move from household to individual voter registration from 2014, voters would no longer be required to co-operate with the electoral registration officer as they seek to compile the annual register. At present voters can be subject to small fines and threatening letters if they do not co-operate, so boosting registration.

As many as 3 million potential voters – mainly poor working-class people, students or ethnic minorities – are not registered. Clegg said on Tuesday: "I have sympathy with the concerns expressed by the Electoral Commission and others about the opt-out proposal, and I am minded to change these provisions when we bring forward the final proposal."

The constitutional affairs minister, Mark Harper, said: "We did have a proposal if someone did not want to be registered – they could tell the registration officer they did not want to be registered and they could be left alone. The reason we put that in was so the electoral registration officer could focus his resources on people for whom it was likely to be able to get on the register. So it was a purely pragmatic thing."

• This article was corrected on 12 October 2011 to amend Jenny Watson's role in the Electoral Commission